Abstract
We experimentally demonstrate 15dB of Raman amplification of 1115nm pulses in an orbital angular momentum mode (OAMM) with charge l=+2, S=+1 in 5m of step-index 25μm-diameter-core fiber. The total output reaches 4.5kW of peak power and 68.5μJ of energy in ∼15 ns pulses at 4kHz repetition rate. An Yb-doped fiber source pumps the Raman amplifier at 1060nm with 60ns pulses. Using a spatial light modulator for modal decomposition, we measure 83% purity for the amplified target OAMM of selected polarization. To the best of our knowledge, this is the first time high energy, peak power, gain, and purity are achieved in a fiber Raman amplifier for a single OAMM.
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